1. Field of the Invention
This invention is directed to a circuit switching device, and more particularly to such a device including a circuit breaker mounted to a pivot arm for physically disconnecting the circuit breaker from a power source and a load. The invention is also directed to a circuit switching device including a circuit breaker and a fuse having a striker pin for tripping the circuit breaker.
2. Background of Information
Circuit breakers are generally used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload fault or a relatively high level short circuit condition. An overload fault condition is normally about 125-600 percent of the nominal current rating of the circuit breaker. A high level short circuit condition can be 1000 percent or more of the nominal current rating. For example, in a bolted three phase line-ground fault, the short circuit current may exceed 100 KA at 480 VAC. Circuit breakers also provide a power circuit electrical disconnection function. In the event of other power circuit problems or during maintenance, for example, the circuit breaker may be used to electrically disconnect a power source from a load.
Drawout circuit breakers are well known in the art. A typical example may be found in U.S. Pat. No. 4,565,908 issued Jan. 21, 1986. Such circuit breakers include a drawout mechanism which permits an operator to physically disconnect the circuit breaker from a power source and a load which are electrically interconnected with the circuit breaker by terminals at the rear of the circuit breaker. The drawout mechanism generally provides an indirect indication (e.g., via a mechanical indicator) that the circuit breaker is at least partially withdrawn from its enclosure and, hence, is physically disconnected from the power source and the load. The mechanical complexity of the drawout circuit breaker leaves room for improvement in terms of cost and application of the physical disconnection function to conventional non-drawout circuit breakers.
It is also known to use a mechanical interlock with the drawout circuit breaker in order to trip such circuit breaker, whenever the power source is electrically interconnected with the load, before the circuit breaker is withdrawn from its enclosure. In this manner, the separable contacts of the circuit breaker, and not the rear terminals, electrically disconnect the load from the power source.
It is further known to use a fuse in combination with a circuit breaker to provide a variety of circuit interrupting characteristics. For example, the circuit breaker may provide a long time delay characteristic having an I.sup.2 t function. The fuse may be connected in series with the circuit breaker and have an I.sup.4 t function.
There remains a need, therefore, for a non-drawout circuit breaker which provides a physical disconnection function.
There is a more particular need for such a circuit breaker which reduces mechanical complexity in comparison to a drawout circuit breaker.
There is another more particular need for such a circuit breaker which reduces cost in comparison to a drawout circuit breaker.
There is yet another more particular need for such a circuit breaker which coordinates the use of a fuse in combination with the physical disconnection function.
There is still another more particular need for such a circuit breaker which reduces the relative size of the housing for such circuit breaker and related switching equipment.